Bob the Angry Flower's Quick Guide to the Apostrophe, You Idiots:
http://angryflower.com/bobsqu.gif
I used to get a bit annoyed when people ended a sentence with a preposition, but it's not really a strict rule. There's also that quote someone mentioned earlier: "Ending a sentence with a preposition is something up with I will not put." I believe it was from Churchill, but that's what they say about every quote.
Also, I read something interesting about people's tendency to say things like "um" and "like" all the time. Apparently it's a more or less necessary part of language; a sort of placeholder in a sentence without which conversations don't move as fluidly.